Spinal bone implant

ABSTRACT

Implantable devices useful for creating bony fusion particularly in intervetebral spinal fusion. The device is formed of bone and has a body portion with an upper flange member and an opposite lower flange member extending from the body portion. The upper and lower flange members are at least partially demineralized to create a flexible ligament extending from the body portion. In one application, the body portion is inserted into a disc space and the flexible ligament is secured to vertebrae on either side of the disc space. Techniques are also disclosed for making the implantable devices and for inserting the implantable device into an intervertebral disc space to promote interbody fusion.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a divisional of U.S. patentapplication Ser. No. 09/777,702 filed on Feb. 6, 2001.

BACKGROUND

[0002] The present invention relates to implantable spinal devices andmethods for their use. More particularly, the present invention relatesto interbody devices formed of bone that may be utilized in spinalfusions.

[0003] A variety of interbody implants are available for spinal fusionprocedures. These implants have been manufactured of various materialsincluding steel, titanium, composites, allograft, xenograft or otherbiocompatible materials, and have the necessary strength to prevent thedisc space from collapsing before fusion has occurred. Other techniquesfor spinal fusion include the placement of bone graft material in thedisc space along with a plate or rod construct that spans the affecteddisc space. One disadvantage to the above devices is that once fusionhas occurred, the implants and hardware used to maintain the stabilityof the segment is unnecessary and remains in the body as a foreignobject.

[0004] Other types of implants have been developed from bio-compatiblemetals which incorporate threads on the outer surface of the implantthat retain the implant in the disc space after it is threaded therein.Still other implants have been developed that are made from bone.Examples of such spacers made from bone having use in spinal proceduresare disclosed in U.S. Pat. No. 5,989,289. The spacers in the '289 patentare provided with vertebral engaging surfaces on the upper and lowerfaces of the implant to resist migration of the implant in the discspace and/or expulsion of the implant from the disc space. While spacersmade of bone offer much improved incorporation in fusion procedures, theinherent brittle nature of bone resulting from a high mineral content,particularly load-bearing cortical bone, severely limits its potentialfor use in applications that require the implant to resist loading otherthan bearing or compression type loading. For example, cortical bonetypically consists of approximately 70% mineral content and 30%non-mineral matter. Of this non-mineral matter, approximately 95% istype I collagen, with the balance being cellular matter andnon-collagenous proteins.

[0005] Bone grafts have commonly been used in a fixed shape, pulverized,or as pliable demineralized bone. One form of a pliable bone graft is ademineralized bone material typically in the form of a sponge or puttyhaving very little structural integrity. While a demineralized bonesegment may retain properties suitable to support bone ingrowth, thestructural properties of the bone are altered by removal of its mineralcontent. Thus, such bone sponges and putties may not typically be usedin load-bearing applications.

[0006] Therefore, there remains a need for bone implants having therequisite load carrying capabilities for applications that require bothbearing or compression load carrying capabilities along withcapabilities for resisting loading other than bearing or compressiontype loading.

SUMMARY

[0007] The present invention is directed to a bone implant having arigid portion for insertion between adjacent bony structures and aflexible portion for securement to the adjacent bony structures.

[0008] According to one aspect of the invention, there is provided animplant that has a body portion positionable in the disc space betweenadjacent upper and lower vertebrae. The implant further includes anupper member and a lower member extending from the body portion alongthe upper vertebral body and the lower vertebral body, respectively. Thebody portion, the upper member, and the lower member are each made frombone material.

[0009] According to another aspect of the invention, there is providedan implant that includes a bone body with a first bearing surface and asecond bearing surface. An upper bone member extends from the body in afirst direction and a lower bone member extends from the body in asecond direction opposite the first direction. The upper and lower bonemembers are at least partially demineralized and flexible.

[0010] According to a further aspect of the invention, there is provideda spinal fusion implant that is adapted for insertion into the spacebetween adjacent first and second vertebral bodies. The implant includesa bone body having a first bearing surface for contacting an endplate ofthe first vertebral body and a second bearing surface for contacting theendplate of the second vertebral body. At least one flexible portionextends from the bone body so that it can be secured to one of the firstor second vertebral bodies outside the disc space.

[0011] According to yet another aspect of the invention, there isprovided a method of preparing a bone implant. The method includesproviding a rigid bone segment having a body portion with an upperbearing surface and opposite lower bearing surface. The rigid bonesegment further includes an upper flange member and an opposite lowerflange member that each extend from the body portion. The upper andlower flange members are at least partially demineralized so as to beflexible.

[0012] According to another aspect of the invention, there is provided amethod of inserting an interbody fusion implant made of bone. The methodincludes: providing an implant formed of bone and having a body portionwith an upper bearing surface and opposite lower bearing surface, therigid bone segment including a flexible upper flange member and anopposite flexible lower flange member each extending from the bodyportion; accessing the disc space between adjacent vertebrae; insertingthe body portion of the implant into the disc space; securing theflexible upper flange member to the upper vertebra; and securing theflexible lower flange member to the lower vertebra.

[0013] According to a further aspect of the invention, a method ofpreparing a bone implant, is provided. The method includes obtaining arigid bone segment and forming from the rigid bone segment an implanthaving a body portion with an upper bearing surface and opposite lowerbearing surface, the rigid bone segment further including an upperflange member and an opposite lower flange member each extending fromthe body portion.

[0014] These and other aspects, advantages, features, embodiments, andobjects of the present invention will be apparent to those skilled inthe art based on the following descriptions of the illustratedembodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is perspective view of an implant according to the presentinvention.

[0016]FIG. 2 is a side elevational view of the implant of FIG. 1inserted in the disc space between adjacent vertebrae.

[0017]FIG. 3 is a side elevational view of another embodiment implantaccording to the present invention.

[0018]FIG. 4 is a perspective view of yet another embodiment implantaccording to the present invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0019] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any such alterationsand further modifications in the illustrated devices, and such furtherapplications of the principles of the invention as illustrated thereinare contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0020] Referring now to FIG. 1, there is shown an implant according toone embodiment of the present invention. Although implants according tothe present invention may have many uses, the embodiment shown in FIG. 1is particularly adapted for promoting interbody fusion in the spine.Specifically, FIG. 1 illustrates a bone implant 10 having a firstsubstantially rigid body portion 12 that extends between a leading end30 and a trailing end 32. Implant 10 further includes at trailing end 32a first or upper flange member 14 that extends upwardly from bodyportion 12 and a second or lower flange member 16 that extendsdownwardly from body portion 12. Preferably, body portion 12 and flangemembers 14, 16 are made from a single piece of bone material, and theflange members are integral with body portion 12. However, otherembodiments contemplate that the flanges are made from a separate pieceof material, such as bone or cartilage, and secured to body portion 12via fasteners or other known bonding technique.

[0021] Flange members 14 and 16 have been at least partiallydemineralized to create flexible flange members extending from rigidbody portion 12. The demineralized portion of implant 10 can extendthrough rigid body portion 12 between upper flange member 14 and lowerflange member 16 as illustrated. Alternatively the demineralized portioncan extend partially into rigid body portion 12, or terminate at thejunction between flange members 14, 16 and rigid body portion 12.Preferably, at least flange members 14 and 16 have been completelydemineralized to provide maximum flexibility. The flexibility created bydemineralization permits flange members 14 and 16 to be movable withrespect to rigid body portion 12 and with respect to each other, andthus function similarly to a ligament extending between and secured tothe adjacent bony structure and to body portion 12.

[0022] Body portion 12 of implant 10 has a cavity 18 which is preferablyderived from the intermedullary canal of the bone from which implant 10is obtained by a cross-cut across the diaphysis of a fibula, femur orlike long bone. Cavity 18 provides an area to receive material thatpromotes bony incorporation and fusion. Prior to positioning bodyportion 12 into the disc space, bone growth promoting material 28 may bepositioned in cavity 18 to encourage bone growth into and through bodyportion 12. Bone growth material can be any type of material known inthe art. As shown further in FIG. 2, upper flange member 14 includes afirst fastener bore 20 for receiving a first fastener 24 and lowerflange member 16 has a second fastener bore 22 for receiving a secondfastener 26. The fasteners of the present invention can be in the formof a threaded screw and made from metal, bone, polymer, bio-absorbablematerial, or other material known in the art.

[0023] As shown in FIG. 2, one specific application of the presentinvention implant 10 contemplates use for fusion of the vertebrae of thecervical spine. In this embodiment implant 10 is obtained from thefibula. Body portion 12 can have any shape, including a specific shapefor use in the cervical region, such as those shapes identified in U.S.Pat. No. 5,989,289 which is incorporated herein by reference in itsentirety. The vertebrae V1 and V2 are accessed from an anterior approachusing known surgical techniques. The disc material is removed and thedisc space height is restored, if necessary, using known surgicaltechniques. Implant 10 is inserted into the prepared disc space. Rigidbody portion 12 is adapted to provide structural support between therespective lower endplate of upper vertebra V1 and the upper endplate ofvertebra V2. In the illustrated embodiment, rigid body portion 12 has aheight H sufficient to provide support for and maintain the desiredspacing between adjacent vertebra V1 and V2. Fusion between vertebrae V1and V2 is obtained with bone growth through cavity 18, which is filledwith bone growth material 28. Fusion between the vertebrae can befurther promoted by reducing the endplates to bleeding bone prior toinsertion of implant 10.

[0024] Implant 10 has upper bearing surface 25 that contacts andsupports upper vertebral body V1 and lower bearing surface 27 thatcontacts and supports implant 10 on lower vertebral body V2. Bodyportion 12 has height H between upper bearing surface 25 and lowerbearing surface 27 that is substantially equal to the height of discspace formed between vertebra V1 and vertebra V2. It will understood bythose skilled in the art that in the preferred embodiment illustratedherein, the height H is substantially constant. Furthermore, while auniform height implant is shown in FIG. 2, it will be understood thatthe implants of the present invention may have a tapered height suchthat the implant could be utilized for establishing or maintaining theproper curvature in the spine. Rigid body portion 12 has sufficientrigidity and structural integrity to substantially maintain height H andto withstand normal forces applied to the spinal column. Flange members14 and 16 need not have such structural requirements, although,preferably, each assists in the implant stability by maintaining rigidbody portion 12 in the disc space between the two vertebrae.

[0025] Fasteners 24 and 26 are placed through the corresponding fastenerbores 20 and 22 in the upper and lower flange members 14 and 16,respectively, to stabilize implant 10 in the disc space. Since flangemembers 14 and 16 are flexible, they can be manipulated and positionedadjacent the vertebral bodies outside the disc space without thecreation of large shear and bending stresses in implant 10 at thejunction between flange members 14, 16 and body portion 12.

[0026] While it is contemplated in one specific embodiment that implant10 have application for fusion of a cervical region of the spine,application at other regions of the spine and at other joints where itis desirable to have a bone implant with a rigid body portion with apair of flexible members extending therefrom are also contemplated. Boneimplant 10 provides the desirable features of being formed of a highlysuccessful bone fusion material, i.e. natural bone, with the advantagesof having flexible members made from bone to secure the rigid bone bodyportion of the implant at the implantation location.

[0027] In another surgical technique, a tensile force can be applied toupper flange member 14 prior to insertion of fastener 24. When fastener24 is secured to vertebra V1, the tensile force is released. Fastener 26can be similarly inserted through bore 22 of a tensioned lower flangemember 16. The pre-tensioned upper flange member 14 and pre-tensionedlower flange member 16 thus apply a compressive load on body portion 12in the disc space, further promoting fusion and incorporation of implant10 and inhibiting expulsion of implant 10 from the disc space.

[0028] Referring now to FIG. 3, a further embodiment implant is shownand designated as 50. Implant 50 is substantially identical to implant10. Implant 50 includes rigid body portion 52 with flexible upper flangemember 54 and flexible lower flange member 56 extending therefrom. Afirst fastener bore 60 is formed through upper flange member 54 and asecond fastener bore 62 is formed through lower flange member 56. Bodyportion 52 includes a cavity 58 in which bone growth material 64 isplaced.

[0029] Body portion 52 further includes a number of upper boneengagement ridges 68 formed on and extending upwardly from upper bearingsurface 66 with an identical set of lower ridges 72 formed on andextending downwardly from lower bearing surface 70. It will beunderstood that while ridges have been shown in the illustratedembodiment, it is contemplated that there are a variety of structures,which could provide a surface for effective engagement with thevertebral bodies to limit expulsion from the disc space. Examples ofsome such further structures are discussed in U.S. Pat. No. 5,989,289.Further, the endplates or bearing surfaces of the adjacent bonystructure can be roughened or otherwise shaped to retain the bodyportion 52 in its inserted position.

[0030] Referring now to FIG. 4, there is shown another embodimentimplant 80 for use in vertebral fusion procedures that has particularapplication in a posterior approach to the disc space, although implant80 may be used in other approaches, including anterior and lateralapproaches. Implant 80 has a rigid body portion 82 with an upper flangemember 84 and a lower flange member 86 each extending from rigid bodyportion 82 at its trailing end. Implant 80 does not have a cavity andcan therefore have a width that is less than the width of implants 10and 50. Access to the disc space between adjacent vertebra is achievedas known in the art. Examples of such techniques and posterior boneimplants are discussed in PCT Publication No. WO 00/24327, which isincorporated herein by reference in its entirety. Once access isachieved, the disc space is distracted if necessary. Implant 80 is movedinto the disc space with body portion 82 positioned between the adjacentvertebrae and upper flange member 84 and lower flange member 86positioned adjacent the vertebral bodies outside the disc space. Oncebody portion 82 is secured in the disc space D, fasteners can be used tosecure the flange members to the respective adjacent vertebral body. Itwill be understood that a second implant can be placed in the disc spaceadjacent the first inserted implant to provide further stability.

[0031] Although not illustrated, the implants of the present inventioncan have a slot or threaded bore for engaging a driving tool adapted toposition and push the implant into the disc space.

[0032] The bone for the implants of present invention is preferablyselected from one of the femur, tibia, fibula radius, or ulna or otherbone segment having the requisite cortical bone strength. It is furthercontemplated that implant 10 can be autograft, allograft, or xenograftbone with the bone being treated as known in the art for subsequentimplantation into the recipient. Specifically, the bone implant may beselected from donor bone having sufficient resistance to compressionbetween the upper and lower surfaces to find application in the intendedenvironment.

[0033] Creation of the demineralized portion of the bone will now bedescribed. The processing involves the use of donor bone with processingin a clean room environment within a bone processing facility. Suchdonor bone may include allograft from human sources or xenograft fromanimal sources. Further, it is contemplated that as technology advancesin the area of bone processing, the donor bone may be generated in themanufacturing process, either by bone growth or by a processing ofconstituent components of bone to create artificial materials havingproperties very similar to bone. More specifically, while any availableallogenic or xenogenic bone stock may be utilized for the procedure,cortical bone is conventionally preferred for spinal fusion for itsstructural properties, although cortical cancellous or cancellous bonemay be used depending upon the particular requirements for the implant.

[0034] In further processing, the connective tissues are removed and thebone is cleaned, rinsed, and defatted using a solvent such as ethanol orhydrogen peroxide. The bone is then machined or otherwise shaped usingconventional techniques to create its final shape. The upper and lowerflange members and, if require, the body portion are demineralized tocreate the required flexible capability. Penetration of thedemineralization fluid into the bone adjacent the desired area offlexibility may be controlled by hydrostatic pressure thereby limitingthe area of demineralization. The amount of mineral removed from thebone may be adjusted to create the desired amount of flexibility. Thisdemineralization conventionally uses an organic acid such ashydrochloric, nitric, or citric acid. Preferably, the demineralizationsolution comprises 0.1 to 1.0 N HCl, most preferably 0.3 N HCl. If axenograft is used, known techniques on the utilization of organicsolvents to inactivate bone proteins and reduce antigenecity may beapplied at this point. Additionally, the use of glutaraldehyde may takeplace in order to further cross-line the collagen structure followingremoval of the mineral portion. Once the implant has been machined andpartially demineralized, it may be stored prior to insertion.

[0035] Although the above-described processing is disclosed herein as apreferred embodiment, it is contemplated that other suitable processesmay be used.

[0036] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiments have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. An implant, comprising: a body portionpositionable in the disc space between adjacent upper and lowervertebrae; an upper member extending from said body portion along thebody of said upper vertebra; and a lower member extending from said bodyportion along the body of said lower vertebra, wherein said bodyportion, said upper member, and said lower member are each made frombone material.
 2. The implant of claim 1, wherein said upper member andsaid lower member are each flexible permitting movement of said uppermember and said lower members in relation to said body portion.
 3. Theimplant of claim 2, wherein said upper and lower members are made fromat least partially demineralized bone.
 4. The implant of claim 2,wherein said upper and lower members are made from completelydemineralized bone.
 5. The implant of claim 1, wherein said body portionincludes an upper bearing surface and a lower bearing surface separatedby a height, said height adapted to maintain spacing between theadjacent vertebrae.
 6. The implant of claim 5, wherein each of saidupper and lower bearing surfaces includes a bone engaging surface toinhibit expulsion of the implant from the disc space.
 7. The implant ofclaim 1, wherein said body portion is a spinal fusion device and saidbody portion is adapted to maintain a desired spacing between theadjacent vertebrae.
 8. The implant of claim 7, wherein said upper memberand said lower member each have an opening formed therethrough toreceive a fastener to secure the upper and lower member to the bodies ofthe upper and lower vertebrae, respectively.
 9. The implant of claim 1,wherein said body portion, said upper member, and said lower member areformed of a single bone segment.
 10. The implant of claim 1, whereinsaid body portion has a cavity allowing bone growth between the upperand lower vertebrae.
 11. An implant, comprising: a bone body extendingbetween a first bearing surface and a second bearing surface; and anupper bone member extending from said body in a first direction and alower bone member extending from said body in a second directionopposite said first direction, wherein said upper and lower bone membersare at least partially demineralized.
 12. The implant of claim 11,wherein said body is a ring shaped bone segment.
 13. The implant ofclaim 11, wherein: said first bearing surface is adapted to contact anendplate of an upper vertebral body and said second bearing surface isadapted to contact an endplate of an adjacent lower vertebral body; andsaid upper bone member extends alongside said upper vertebral body andsaid lower bone member extends alongside said lower vertebral body. 14.The implant of claim 13, wherein said upper bone member and said lowerbone member each have an opening formed therethrough to receive afastener to secure the implant to the upper and lower vertebral bodies,respectively.
 15. The implant of claim 11, wherein: said bone body ispositionable in the disc space between an upper vertebral body and alower vertebral body; and said upper and lower members act as a ligamentextending between and connecting the upper vertebral body and the lowervertebral body.
 16. The implant of claim 11, wherein said implant isformed of a single segment of bone.
 17. A spinal fusion implant adaptedfor insertion into the space between adjacent first and second vertebralbodies, comprising: a bone body having a first bearing surface forcontacting an endplate of the first vertebral body and a second bearingsurface for contacting an endplate of the second vertebral body; and atleast one flexible portion extending from the bone body for securementto the first and second vertebral bodies outside the disc space.
 18. Thespinal fusion implant of claim 17, wherein said at least one flexibleportion includes a pair of flexible portions.
 19. The spinal fusionimplant of claim 18, wherein said flexible portions act as a ligamentbetween said first and second vertebral bodies.
 20. The spinal fusionimplant of claim 18, wherein the implant has a leading end and anopposite trailing end, and said flexible portions are positionedadjacent said trailing end.
 21. The implant of claim 17, wherein saidimplant is formed from a single segment of bone.
 22. A method ofpreparing a bone implant, comprising: providing a rigid bone segmenthaving a body portion with an upper bearing surface and an oppositelower bearing surface, said rigid bone segment further including anupper flange member and an opposite lower flange member each extendingfrom said body portion; and at least partially demineralizing the upperand lower flange members to create a flexible upper flange member and aflexible lower flange member extending from the rigid body portion. 23.The method of claim 22, wherein said at least partially demineralizingincludes exposing said rigid upper flange member and said rigid lowerflange member to a demineralizing fluid.
 24. The method of claim 22,further including limiting contact of the body portion with thedemineralizing fluid.
 25. The method of claim 24, wherein said limitingutilizes hydrostatic pressure to limit the movement of thedemineralizing fluid into the body portion.
 26. The method of claim 22,further including forming a bone engaging surface on the upper and lowerbearing surfaces of the implant.
 27. The method of claim 26, whereinsaid bone engaging surface is configured to prevent movement of theimplant.
 28. The implant of claim 22, wherein the implant is formed froma single segment of bone.
 29. A method of inserting an interbody fusionimplant made of bone, comprising: providing an implant formed of boneand having a body portion with an upper bearing surface and oppositelower bearing surface, said rigid bone segment further including aflexible upper flange member and an opposite flexible lower flangemember each extending from said body portion; accessing the disc spacebetween adjacent vertebrae; inserting the body portion of the implantinto the disc space; securing the flexible upper flange member to thebody of the upper vertebra; and securing the flexible lower flangemember to the body of the lower vertebra.
 30. The method of claim 29,wherein: securing the upper flexible member includes engaging a fastenerto the body of the upper vertebra through an opening formed through theupper flexible member; and securing the lower flexible member includesengaging a fastener to the body of the lower vertebra through an openingformed through the lower flexible member.
 31. The method of claim 29,wherein accessing the disc space includes accessing the disc space viaan anterior approach.
 32. The method of claim 29, wherein accessing thedisc space includes accessing the disc space via a posterior approach.33. The method of claim 29, wherein accessing the disc space includesaccessing the disc space between adjacent cervical vertebrae.
 34. Amethod of preparing a bone implant, comprising: obtaining a rigid bonesegment; and forming from said rigid bone segment an implant having abody portion with an upper bearing surface and opposite lower bearingsurface, said rigid bone segment further including an upper flangemember and an opposite lower flange member each extending from said bodyportion.
 35. The method of claim 34, further comprising at leastpartially demineralizing the upper and lower flange members to create aflexible upper flange member and a flexible lower flange memberextending from the body portion.
 36. The method of claim 34, wherein:the upper and lower bearing surfaces each extend between a leading endand a trailing end of the body portion; and the upper and lower flangemembers each extend from the body portion at the trailing end.
 37. Themethod of claim 34, wherein the upper and lower bearing surfaces extendsubstantially parallel to one another.
 38. The method of claim 34,further including forming a bone engaging surface on the upper and lowerbearing surfaces of the body portion.
 39. The implant of claim 34,wherein the implant is formed from a single segment of bone.